Until recently, polyhydroxystyrenes or derivatives thereof in which the hydroxyl groups are protected with an acid dissociable, dissolution inhibiting group, which display high transparency relative to a KrF excimer laser (248 nm), have been used as the resin component of chemically amplified resists.
However, these days, the miniaturization of semiconductor elements has progressed even further, and the development of processes using ArF excimer lasers (193 nm) is being vigorously pursued.
For processes using an ArF excimer laser as the light source, resins comprising a benzene ring such as polyhydroxystyrene have insufficient transparency relative to the ArF excimer laser (193 nm).
In order to resolve this problem, resins containing no benzene rings, but instead comprising a unit derived from a (meth)acrylate ester incorporating an adamantane ring within the principal chain are attracting considerable interest, and many materials have already been proposed (Japanese Patent (Granted) Publication No. 2881969, Japanese Unexamined Patent Application, First Publication No. Hei 5-346668, Japanese Unexamined Patent Application, First Publication No. Hei 7-234511, Japanese Unexamined Patent Application, First Publication No. Hei 9-73173, Japanese Unexamined Patent Application, First Publication No. Hei 9-90637, Japanese Unexamined Patent Application, First Publication No. Hei 10-161313, Japanese Unexamined Patent Application, First Publication No. Hei 10-319595 and Japanese Unexamined Patent Application, First Publication No. Hei 11-12326). The term (meth)acrylate ester refers to acrylate esters or methacrylate esters.
In these publications, as can be seen in Japanese Unexamined Patent Application, First Publication No. 2001-131232 and Japanese Unexamined Patent Application, First Publication No. 2001-142212, but also true for the preceding technology described above, the materials comprising a unit derived from a (meth)acrylate ester within the principal chain are proposed without any discrimination between the acrylate ester and the methacrylate ester, although in the examples, materials with methacrylic acid as the principal chain are used, and practical applications also utilize materials with methacrylic acid in the principal chain.
The reason for this observation is that a resin with a conventional acrylate ester as the principal chain (hereafter, simply referred to as an acrylate ester resin), as disclosed in the above publications, displays a lower Tg value than a resin with a methacrylate ester as the principal chain (hereafter, simply referred to as a methacrylate ester resin). More specifically, this Tg value is considerably lower than conventional prebake temperatures of 120 to 140° C. and PEB (post exposure baking) temperatures of 120 to 130° C. required in chemically amplified resist compositions for vaporizing the solvent and forming the resist film, and enabling the acid generated from the acid generator to eliminate the acid dissociable, dissolution inhibiting groups, and in these processes, or even in processes with a lower temperature requirement of, for example, approximately 20° C. lower, formation of a resist pattern was impossible.
However, with the development of different etching films in recent years, a variety of etching gases can now be used, and as a result, a new problem has arisen in that surface roughness appears on the resist film following etching.
This surface roughness is different from conventional dry etching resistance, and in a film etched using a resist pattern as a mask, appears as distortions around the hole patterns in a contact hole pattern or as line edge roughness in a line and space pattern. Line edge roughness refers to non-uniform irregularities in the line side walls.
Furthermore, in addition to the surface roughness generated following etching, line edge roughness also occurs in the resist pattern following developing. This line edge roughness following developing also appears as distortions around the hole patterns in a contact hole pattern or as non-uniform irregularities in the line side walls in a line and space pattern.
In addition, the design rules required in modern semiconductor element production continue to become more stringent, and a resolution of no more than 150 nm, and in the vicinity of 100 nm is necessary, and further improvements in resolution are keenly sought. In resist patterns requiring this type of high resolution, distortions around the hole patterns or line edge roughness such as that described above becomes a larger problem than in conventional patterns.
In addition, resolving line slimming is also desirable. Line slimming is a phenomenon in which during observation of a resist pattern using a scanning electron microscope (SEM), the formed resist pattern shrinks and narrows. The cause of line slimming is reported to be due to the fact that when the formed resist pattern is exposed with the electron beam used in a SEM, a cross linking reaction occurs, causing slimming [Journal of Photopolymer Science Technology, Vol. 13, No. 4, page 497 (2000)].
As the design rules become tighter, this type of line slimming problem has an increasing effect on the production of semiconductor elements, and consequently improvements are keenly sought.